In this project structure and expression of period gene in honeybees, Apis cerana japonica were investigated to reveal the molecular mechanism of temporal division of behavioral activity in the field, which is considered to be one of the basis of biodiversity maintenance in the multi-species coexistence. At first the characteristics of circadian rhythm in the honeybee were investigated using individual workers and a colony that was entrained in Zootron. Then period gene encoding cDNA was cloned by use of PCR strategy, and found fours kinds of spliced alternative variants exist. To investigate the molecular mechanism of formation of period m-RNA variants, genomic structure of the honeybee was analysed on the encoding period gene region including introns. Further RT-PCR experiments showed tissue specific expression patterns in worker bees. The results obtained suggested that there are some slave peripheral clocks in addition to the main clock localized in the brain.